The wind turbine generator is an apparatus in which a rotor head having wind turbine blades receives wind power and rotates, and electricity is generated by a power generator that is driven by accelerating this rotation by a gear box.
The rotor head is mounted on an end of a nacelle that is disposed on a wind turbine tower (“tower”, hereinafter) and is capable of yaw-slewing, and the rotor head is supported such that the rotor head can rotate around a substantially horizontal lateral rotation axis.
A conventional wind turbine generator includes a pitch control system that varies a pitch angle of the wind turbine blades in accordance with a wind speed. The pitch control system sets an optimal pitch angle between the wind turbine blades in accordance with the wind speed, and controls a rotation speed of the rotor head.
In order to adjust the pitch angle of the wind turbine blades by the pitch control system, a blade rotating ring bearing that turnably supports the wind turbine blades with respect to the rotor head is used. A rolling bearing in which rolling bodies (ball bearing or rollers and the like) are disposed between an inner race and an outer race is employed as the blade rotating ring bearing.
In the blade rotating ring bearing, to prevent leakage of lubricant oil (grease) that lubricates a bearing sliding portion, oil seals are provided on both ends of bonding surfaces between the inner race and the outer race that constitute the bearing. That is, the bonding surfaces in which rolling bodies-holding surfaces (an outer peripheral surface of the inner race and an inner peripheral surface of the outer race) that sandwich the rolling bodies are opposed to each other at a predetermined gap from each other have exits of the gap that open toward both ends of the outer race and the inner race, and the exits are sealed by the oil seals.
The following patent literature 1 discloses to employ a labyrinth seal structure for preventing water or a foreign matter from entering a bearing box of the rolling bearing that is lubricated with grease.